1. Field of the Invention
This invention relates to crystalline aluminosilicate zeolites and to the synthesis thereof. It more particularly relates to the synthesis of a zeolite containing an outer shell free from aluminum. The invention further relates to the product of such synthesis.
2. Discussion of the Prior Art
Certain of the zeolites disclosed herein and their synthesis are well known. Examples are ZSM-5 and ZSM-11. These zeolites are fully described in U.S. Pat. Nos. 3,702,886 and 3,709,979. They are known to have catalytic capabilities for various conversion reactions. Because of their ordered, porous structure, creating small interconnected cavities, they are selective toward certain molecules. That is to say, the pores accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions. However, no known art discloses or suggests increasing selectivity by essentially inactivating the surface of the catalyst with an isocrystalline layer of aluminum-free zeolite.